This invention relates to improvements in variable pulleys for flat belt transmission systems of the nature disclosed in U.S. Pat. No. 4,295,836, Oct. 20, 1981, Emerson L. Kumm.
As shown in the said patent, the variable pulley consists of two pulley sheaves concentric with each other but axially spaced to provide the necessary space for receiving the driving belt. Each pulley sheave is comprised of two pulley disks each of which has logarithmic spiral grooves or approximation thereof extending from near the center of the pulley disk to adjacent its periphery. The logarithmic spiral grooves in the inner and outer disks of each pulley sheave extend in opposite directions so that the grooves of respective inner and outer disks, in effect, intersect with each other.
In the interest of simplicity, throughout this specification, the word -grooves- will be used instead of logarithmic spiral grooves in most instances. It will be understood that -logarithmic spiral- is intended.
The grooves in the inner disks of the two pulley sheaves extend in the same direction and the grooves in the outer ones of the two pulley sheaves extend in an opposite direction. Drive elements which are engaged by the drive belt extend between the pulley sheaves on each side of the pulley and are maintained in their radial positions by the intersections of the grooves. By rotating the two inner disks relative to the two outer disks the radial position of the drive elements is varied, that is, it is increased or decreased depending upon the direction of relative rotation. In this manner the variability of the pulley to change the radius of the drive belt elements is achieved.
The pulleys and belt operate in a dry, unlubricated condition in order to obtain high friction coefficients between the belt and the belt drive elements in the pulleys.
The two ends of each belt drive element located in the intersections of the grooves bear loads to and from the belt and pulley sheaves and are thus subject to substantial wear as are the surfaces of the grooves themselves when sliding movements occur under loaded conditions. The drive elements, of necessity, are not permitted to rotate about their own axes in order to achieve rotation of the pulley under the influence of the drive belt. However, the drive belt exerts a tangential or frictional force on the drive elements in addition to the radial forces existing between the belt and drive elements. The tangential force gives rise to a moment trying to rotate the drive elements. All of these forces contribute to wearing the bearing ends of the drive elements. The tangential force gives rise to a moment trying to rotate the drive elements. All of these forces contribute to wearing the bearing ends of the drive elements located at the intersections of the grooves as well as the disk grooves when the drive elements are changed in radial position.